PROJECT SUMMARY/ABSTRACT Project IV: Tackling Heterogeneity of Cognitive Trajectory in Lewy Body Disorders Project IV Leader: Alice Chen-Plotkin; Co-Leaders: Daniel Weintraub, Rizwan Akhtar While patients with Lewy body disorders (LBD) share the core feature of deposition of misfolded alpha-synuclein (aSyn) into neuropathological inclusions, they exhibit pronounced heterogeneity in both initial clinical phenomenology, as well as in trajectory of outcome. Specifically, among human patients with aSyn inclusions in neurons (or neuronal synucleinopathy), some manifest predominantly with cognitive symptoms and dementia from disease onset ? resulting in a clinical diagnosis of Dementia with Lewy bodies (DLB). Others manifest predominantly with motor symptoms ? resulting in a clinical diagnosis of Parkinson?s Disease (PD). Among PD patients, some subsequently develop significant cognitive decline and eventual dementia (Parkinson?s Disease with Dementia, or PDD), while others do not. The reasons for these differences in phenomenology among synucleinopathy patients are not well understood. Project IV, like Projects I, II, and III, investigates the role of aSyn in the Alzheimer?s Disease related dementias (ADRD), in the context of living patients who manifest with DLB vs. PD vs. PDD vs. AD. This project aims to define endophenotypes within the LBD vs. AD spectrum using objectively-measured biomarker characteristics. We use both unbiased screening approaches and hypothesis-driven approaches to develop genetic and biochemical biomarkers in three Aims: Specific Aim 1: Develop biochemical biomarkers of differential PD cognitive progression. Through unbiased screening of >1000 plasma proteins in >300 PD patients from multiple cohorts, we have derived a candidate list of 10 plasma proteins whose baseline levels associate with subsequent cognitive decline. We will validate these markers in >1000 additional PD subjects, developing multi-protein classifier panels for accurate prediction of cognitive trajectory. We will characterize these proteins in comparator groups of DLB and AD patients, as well as neurologically normal controls. Specific Aim 2: Investigate causal influences on cognitive trajectory among LBD patients using Mendelian randomization. We will use Mendelian randomization (MR) to test the hypotheses that candidate biochemical biomarkers and AD-related disease processes influence cognitive trajectory in LBD. To do this, we will use as instrumental variables for MR single nucleotide polymorphisms (SNPs) nominated from (1) their relationships with protein levels of candidate biochemical biomarkers or (2) their genomewide association with AD risk. These SNPs may then be developed as genetic biomarkers predicting cognitive trajectory in LBD. Specific Aim 3: Define the clinical correlates of different strains of aSyn. We will use enzyme-linked immunosorbent assays (ELISAs) developed with antibodies raised to different conformations of aSyn ? ?strains? as defined in Project I ? to test the hypothesis that different strains of aSyn result in differential development of cognitive features among the synucleinopathies PD without dementia, PDD, and DLB. We will characterize AD and neurological normal controls as comparator groups.